1. Field of the Invention
The present invention relates to a mirror and an optical scanning device for scanning a scanning surface with a light in an image forming apparatus.
2. Description of the Related Art
A conventional image forming apparatus employing the Carlson process forms an image by scanning the surface of a rotating photosensitive element with a light beam to form a latent image, developing the latent image with toner to form a toner image, and then transferring the toner image onto a recording medium (hereinafter, “sheet”). Such an image forming apparatus is often used as an on-demand printing system for simple printing. In recent years, a color image forming apparatus having such a configuration has been widely used.
One type of color image forming apparatus includes a single photosensitive element for a plurality of colors. Such an image forming apparatus forms a plurality of toner images corresponding to the colors on the surface of the photosensitive element in a superimposed manner, and transfers the toner images formed on the surface of the photosensitive element onto a sheet. The other type of color image forming apparatus includes a plurality of photosensitive elements each corresponding to a different color (hereinafter, “tandem-type image forming apparatus”). The tandem-type image forming apparatus forms a corresponding toner image on the surface of each of the photosensitive elements, and transfers the toner images on the surfaces of the photosensitive elements onto a sheet in a superimposed manner. Because both types of color image forming apparatuses form the toner images in a superimposed manner to form a full color image, it is necessary to transfer the toner images onto a sheet at predetermined positions with high accuracy.
The accuracy of forming the toner images on the sheet depends on relative positions between a shaping optical system that shapes a light beam emitted from a light source and an optical element included in a projection optical system that projects the light beam onto the photosensitive element. Therefore, an optical element, such as a mirror disclosed in, for example, Japanese Patent No. 2637016 or Japanese Patent Application Laid-open No. 2000-155204, needs to be set in an appropriate position with respect to the shaping optical system with high accuracy.
To reduce the number of components used in the color image forming apparatus and facilitate assembling the components, the above mirror is arranged in the color image forming apparatus such that a part of the mirror is attached to a supporting unit arranged in a housing accommodating the optical system or the like. In such a case, because it is necessary to prevent occurrence of registration misalignment or color misalignment due to change of the relative positions between the mirror and the shaping optical system, hydrophilic nature of the surface of the mirror on the attachment side (hereinafter, “attachment surface”) needs to be increased to improve attachment strength of the mirror.